Yung-Ruei Chang

High-Efficiency Power Conversion System for Kilowatt-Level Stand-Alone Generation Unit With Low Input Voltage

This paper mainly focuses on the development of a high-efficiency power conversion system for kilowatt-level stand-alone generation units with a low output voltage, such as photovoltaic modules, fuel cells, and small-scale wind generators, and it aims at having the same output ac voltage, i.e., 110 Vrms/ 60 Hz as the utility power for the utilization of a stand-alone power supply. This high-efficiency power conversion system includes one high-efficiency high-step-up dc-dc converter and one soft-switching dc-ac current-source inverter. This dc-dc converter is capable of solving the voltage spike problem while the switch is turned off, and it can achieve the objectives of high efficiency and high voltage gain. Because the techniques of soft switching and voltage clamping are used in the dc-ac current-source inverter, the conversion efficiency could greatly be improved. The effectiveness of the designed circuits is verified by experimentation, and the maximum efficiency of the entire high-efficiency power conversion system is over 91% based on the experimental measurements.

Design of High-Performance Stand-Alone and Grid-Connected Inverter for Distributed Generation Applications

In this study, a high-performance inverter, including the functions of stand-alone and grid-connected power supplies, is developed so that distributed generation units can operate individually or in a microgrid mode. In the stand-alone power-supply mode, the output ac voltage can supply to ac loads. In the grid-connected power-supply mode, the goal of power management can be achieved by controlling the amplitude and direction of the output current in the inverter. An adaptive total sliding-mode control (ATSMC) scheme is designed for the proposed high-performance inverter with a full-bridge framework. As a result, the proposed high-performance inverter with the ATSMC scheme has the output voltage with a low total harmonic distortion in the stand-alone power-supply mode and the output current with a high power factor in the grid-connected power-supply mode to provide an ac output with high-performance power quality. The effectiveness of the proposed high-performance inverter with the ATSMC is verified by experimental results of a 5-kW prototype, and the merit of the proposed ATSMC scheme is indicated in comparison with conventional proportional-integral and proportional-resonant control strategies.

DC-Bus Voltage Control With a Three-Phase Bidirectional Inverter for DC Distribution Systems

This paper presents dc-bus voltage control with a three-phase bidirectional inverter for dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification modes with power factor correction. The proposed control includes two approaches, one line-cycle regulation approach (OLCRA) and one-sixth line-cycle regulation approach (OSLCRA), which take into account dc-bus capacitance and control dc-bus voltage to track a linear relationship between the dc-bus voltage and inverter inductor current. Since both of the approaches require the parameter of dc-bus capacitance, this paper first presents determination of dc-bus capacitor size and an online capacitance estimation method. With the OLCRA, the inverter tunes the dc-bus voltage every line cycle, which can reduce the frequency of operation-mode change and current distortion. The OSLCRA adjusts current command every one-sixth line cycle to adapt to abrupt dc-bus voltage variation. The two approaches together can prevent dc-bus voltage from wide variation and improve the availability of the dc distribution systems without increasing dc-bus capacitance. Experimental results measured from a three-phase bidirectional inverter have verified the feasibility of the discussed control approaches.

High Step-Up Bidirectional Isolated Converter With Two Input Power Sources

The objective of this paper is to develop a high step-up isolated converter with two input power sources. The proposed converter has two input ports for simultaneously converting two different input power sources with low voltages to a stable output power with a high voltage. Moreover, the demand of bidirectional power flow, which is dependent on the power management for charging and discharging power storage mechanisms, can also be satisfied in the proposed converter. According to various situations, the operational states of the proposed converter can be divided into three states, including a stand-alone state, a united power supply state, and a charge and discharge state. The effectiveness of the designed circuit topology is verified by experimental results, and the goals of high-efficiency conversion, high step-up ratio, and bidirectional power flow can be achieved by the proposed converter operation.

MPPT Battery Charger for Stand-Alone Wind Power System

In this paper, a buck-type power converter as the battery charger for the stand-alone wind power system is proposed. The proposed power converter can harvest the maximum power from the wind turbine while generating pulsating current for the battery bank to improve the charging efficiency. The maximum power point tracking function is realized by the constant on-time control, the circuit parameter design of the power converter, and the characteristics of wind turbine. The pulsating battery charging current is implemented by the discontinuous conduction mode operation of the proposed power converter. Also, the overspeed protection of the wind turbine can be naturally achieved when high power output occurs. Circuit simplicity and high reliability are the major advantages of the proposed power converter. Hardware experimental results from a 400-W prototype circuit are presented to verify the performance of the proposed power converter.

Newly Designed ZVS Multi-Input Converter

A newly designed zero-voltage-switching (ZVS) multi-input converter is proposed in this paper. The converter can boost the different voltages of two power sources to a stable output voltage. An auxiliary circuit is employed for achieving turn-on ZVS of all switches in the proposed converter. According to various situations, the operational states of the proposed converter can be divided into two states, including a single-power-supply and a dual-power-supply state. In the dual-power-supply state, the input circuits connected in series together with the designed pulsewidth modulation can greatly reduce the conduction loss of the switches. In addition, the effectiveness of the designed circuit topology and the ZVS properties are verified by experimental results, and the goal of high-efficiency conversion can be obtained.

Simplified Reactive Power Control for Single-Phase Grid-Connected Photovoltaic Inverters

The objective of this paper is to propose a simplified reactive power control (SRPC) strategy for single-phase grid-tied photovoltaic (PV) inverters. With the proposed SRPC strategy, a cost-effective microcontroller can be adopted to achieve an effectively reactive power control. Moreover, the current-mode asynchronous sigma-delta modulation (CASDM) is adopted to enhance the current controls dynamic response and reduce both the current harmonic distortion and electromagnetic interference. In this paper, the operational principle of the proposed SRPC is introduced. Then, the small signal analysis for the PV inverter with the CASDM is presented. Finally, a 1-kVA single-phase PV inverter was built to verify the performance of the proposed control strategy.

Intelligent Optimal Energy Management System for Hybrid Power Sources Including Fuel Cell and Battery

In this study, an intelligent optimal energy management system is designed for hybrid power sources including a fuel cell (FC) system and a battery module. In the proposed intelligent optimal energy management system, a simple fan temperature control is introduced to reduce the possible energy waste during the startup of the FC system. Moreover, a fuzzy hydrogen control is designed to manipulate the FC system stably and generate the same unit power with less hydrogen. In addition, a stable adaptive current-voltage fast-charging control is investigated to improve the charge speed in conventional constant current/constant voltage (CC/CV) scheme with proportional-integral control. The objectives of fast charging, energy saving, power source protection, and system stability assurance can be simultaneously achieved. Furthermore, the effectiveness of the proposed intelligent optimal energy management system is verified by experimental results. Its merits are indicated by comparing a conventional management system without the fan temperature control and with a fixed hydrogen pressure and a CC/CV charging framework.

Two-Phase Modulated Digital Control for Three-Phase Bidirectional Inverter With Wide Inductance Variation

This paper presents two-phase modulated digital control for a three-phase bidirectional inverter with wide inductance variation in dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification with power factor correction. With the proposed control, the inverter can track its sinusoidal reference currents, and it is allowed to have wide inductance variation, reducing core size significantly. The control laws based on space-vector pulsewidth modulation are first derived with either an accurate approach or an approximated one, and the gate signals were then derived based on two-phase modulation for lower switching loss and switching noise spectra. Determination of control parameters and stability analysis are also presented. In the design and implementation, the inductances corresponding to various inductor currents were measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. Measured results from a 10 kVA 3φ bidirectional inverter have been presented to confirm the feasibility of the discussed control approaches.

Reactive Power Control of Three-Phase Grid-Connected PV System During Grid Faults Using Takagi–Sugeno–Kang Probabilistic Fuzzy Neural Network Control

An intelligent controller based on the Takagi-Sugeno-Kang-type probabilistic fuzzy neural network with an asymmetric membership function (TSKPFNN-AMF) is developed in this paper for the reactive and active power control of a three-phase grid-connected photovoltaic (PV) system during grid faults. The inverter of the three-phase grid-connected PV system should provide a proper ratio of reactive power to meet the low-voltage ride through (LVRT) regulations and control the output current without exceeding the maximum current limit simultaneously during grid faults. Therefore, the proposed intelligent controller regulates the value of reactive power to a new reference value, which complies with the regulations of LVRT under grid faults. Moreover, a dual-mode operation control method of the converter and inverter of the three-phase grid-connected PV system is designed to eliminate the fluctuation of dc-link bus voltage under grid faults. Furthermore, the network structure, the online learning algorithm, and the convergence analysis of the TSKPFNN-AMF are described in detail. Finally, some experimental results are illustrated to show the effectiveness of the proposed control for the three-phase grid-connected PV system.